The present invention pertains to alkylthioalkanoyloxyalkyl and alkylthioalkyl derivatives of N-heterocyclic moieties and to compositions which are stabilized by these derivatives against the deleterious effects of heat and oxygen and against discoloration.
Of particular interest are polyolefin resin compositions containing said derivatives which are stabilized against thermal aging and light induced degradation. Polyolefin resins have inherently good mechanical and physical properties and are useful as resin substrates for molded articles, films and fibers. Other resins of particular interest include thermoplastic elastomers, ABS resins, polystyrene, and other hydrocarbon polymers.
In an attempt to permit these resins to exhibit the full measure of their inherent properties, it has been customary to add one or more stabilizers to the resins to overcome their susceptibility to oxidative and thermal degradation.
Phenolic antioxidants have long been used in the art as such stabilizers with varying degrees of success as seen in U.S. Pat. No. 3,285,855. It was shown in U.S. Pat. No. 2,956,982 that the dialkyl esters of .beta.-thiodipropionic acid were also effective stabilizers for polyolefin resins. The combination of a lesser amount of a phenolic antioxidant with a small quantity of a dialkyl .beta.-thiodipropionate was found to have a synergistic effect on the level of stabilization of such compositions superior to the use either of the phenolic antioxidant alone or the dialkyl .beta.-thiodipropionate alone at the given concentration, (U.S. Pat. No. 3,285,855).
Other sulfur containing compounds have been discovered which also exhibit synergistic stabilization effects in combination with phenolic antioxidants in polyolefin compositions. These include the dialkyl alkylthiosuccinates (U.S. Pat. No. 3,345,327); the thiodialkanoate polyesters (U.S. Pat. No. 3,157,517 and U.S. Pat. No. 3,378,516); the derivatives of N',N",N'"-tris(3-mercaptopropionyl)-hexahydros-triazine (U.S. Pat. No. 3,538,092); the pentaerythritol or trimethylolpropane esters of alkylthioalkanoic acids (U.S. Pat. No. 3,629,194 and U.S. Pat. No. 3,758,549); and the 2,4,6-tris(alkylthioalkylthio)-1,3,5-triazines (U.S. Pat. No. 3,652,561).
While all of these materials exhibit useful synergistic stabilization effects in the presence of phenolic antioxidants in polyolefin or other hydrocarbon systems which are subject to oxidative and/or thermal deterioration, the dialkyl .beta.-thiodipropionates (particularly the dilauryl and especially the distearyl esters) have become the thiosynergists of choice in the art enjoying widespread use.